Field of the Invention
The present invention relates to an organic light-emitting display device, and more particularly, to an organic light-emitting display device with a structure on a bank to cut off an organic material.
Discussion of the Related Art
Recently, as the information age has fully arrived, the field of displays that visually display electrically conveyed information signals has developed rapidly. In response to this, various kinds of flat panel display devices having excellent characteristics, such as a small thickness, a low weight, and low power consumption, have been developed and have rapidly replaced existing cathode ray tubes (CRTs).
Representative examples of such flat panel display devices may include a liquid crystal display (LCD) device, a plasma display panel (PDP) device, a field emission display (FED) device, and an organic light-emitting display (OLED) device.
Among these, the organic light-emitting display device is considered a competitive application because it does not require a separate light source and enables realization of a compact device design and vivid color display.
The organic light-emitting display device includes organic light-emitting elements, which are independently driven on a per-sub-pixel basis. Such an organic light-emitting element includes an anode, a cathode, and a plurality of organic layers between the anode and the cathode.
The organic layers include a hole injection layer, a hole transport layer, an organic light-emitting layer, and an electron transport layer, which are sequentially disposed from the anode. Among these, the organic light-emitting layer substantially functions to emit light as the energy of excitons, produced via the combination of holes and electrons, falls down to the ground state. The other layers function to assist in the transport of holes or electrons to the organic light-emitting layer.
In addition, in the organic light-emitting display device, for color display, sub-pixels are divided into red, green, and blue sub-pixels, and on a per-sub-pixel basis, an organic light-emitting layer having the color of a corresponding sub-pixel is formed. Generally, deposition using a shadow mask is used to form the organic light-emitting layer.
However, when the shadow mask has a large area, the shadow mask may droop due to the weight thereof, and thus may cause deterioration in a yield rate when used multiple times. Therefore, the other organic layers excluding the light-emitting layer are continuously formed in common in the respective sub-pixels without the shadow mask.
However, since current may flow laterally through the resulting common layer of the sub-pixels that is continuously formed in a plane, lateral current leakage may occur.
FIG. 1 is a cross-sectional view illustrating a lateral current leakage phenomenon in a conventional organic light-emitting display device. Considering one form of the conventional organic light-emitting display device, as illustrated in FIG. 1, in each sub-pixel on a substrate 10, a first electrode 11, a bank 12, which is superimposed on the edge of the first electrode 11 and defines an emission portion, and a hole injection layer 13 and a hole transport layer 14, which cover the first electrode 11 and the bank 12, are formed in sequence. In addition, light-emitting layers 16 and 17, an electron transport layer 18, and a second electrode 19 are formed in sequence above the hole transport layer 14.
In addition, in a red sub-pixel in which a light-emitting area between the first and second electrodes 11 and 19 is formed higher than those of other sub-pixels according to resonance conditions, in order to match such a light-emitting height, an auxiliary hole transport layer 15 may be further provided between the hole transport layer 14 and the red light-emitting layer 16. The position of a light-emitting layer at which the maximum wavelength is obtained may be differently set between the first and second electrodes 11 and 19 for each color of light. A red light-emitting layer may be located at the highest height, a green light-emitting layer may be located at the second highest height, and a blue light-emitting layer may be located at the lowest height. Accordingly, a green sub-pixel may further include an auxiliary hole transport layer between the hole transport layer and the green light-emitting layer, and the auxiliary hole transport layer provided in the green sub-pixel may be thinner than the auxiliary hole transport layer 15 provided in the red sub-pixel.
However, as illustrated in FIG. 1, in the conventional organic light-emitting display device, upon low-gradation blue illumination, a phenomenon in which an adjacent red sub-pixel is also turned on occurs. This is caused by a phenomenon in which, although a voltage is applied between the first electrode and the second electrode of only a blue sub-pixel in order to emit pure blue light, current flowing through a vertical electric field between the first electrode (anode) and the second electrode (cathode) of the blue sub-pixel when turned on leaks laterally through a common layer, causing an adjacent sub-pixel to be turned on.
The lateral current leakage, in particular, is clearly visible in a low-gradation display. This is because, when current, which horizontally flows in the blue sub-pixel, flows laterally to common organic layers, the adjacent red sub-pixel, which is in an off state, acts as if it were turned on. In this case, color purity may be deteriorated, and the display of pure blue gradation is difficult.
This is because the drive voltage required for red illumination is lower than the drive voltage required for blue illumination, and therefore, causes a similar illumination effect even by a small amount of leaked current.
In particular, such other color illumination caused by lateral current leakage may cause color mixing in a low-gradation display, which may prevent a desired color from being normally displayed.
In addition, the lateral current leakage may have a greater effect on the adjacent sub-pixel when the hole mobility of the common organic layer is increased.